1. Field of the Invention
The present invention relates to a sensor equipped wheel support bearing assembly having a load sensor built therein for the detection of a load acting on a bearing assembly of a vehicle wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, a wheel support bearing assembly equipped with a sensor for detecting the rotational speed of each of vehicle wheels has hitherto been well known in the art. While the automobile traveling safety precaution is generally taken by detecting the rotational speed of the respective vehicle wheel arranged in various locations, it is not sufficient with only the rotational speeds of the vehicle wheels and, therefore, it is desired to achieve a control with the use of other sensor signals for safety purpose.
In view of the above, it may be contemplated to achieve the vehicle stability control based on a load acting on each of the vehicle wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along horizontally inclined road surfaces or on the front wheels during braking, and, thus, a varying load acts on the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the stability control of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of sinking of the front wheels during braking, and prevention of sinking of the vehicle wheels brought about by an uneven distribution of live loads) can be accomplished. However, an appropriate space for installation of the load sensor for detecting the load acting on the respective vehicle wheel can hardly be found and, therefore, the stability control through the detection of the load is difficult to realize.
Also, in the event in the near future the steer-by-wire is introduced and the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, is increasingly used, transmission of information on the road surface to the steering wheel held by a driver, by detecting a wheel axis direction load would come to be required.
In order to meet those needs hitherto recognized, a wheel support bearing assembly has been suggested, in which a strain gauge is affixed to an outer ring of the wheel support bearing assembly so that strains occurring in the outer ring can be detected when the rolling elements move past the outer ring. (See, for example, the Patent Documents 1 and 2 listed below.)                [Patent Document 1] Japanese Laid-open Patent Application No. 2003-530565        [Patent Document 2] International Publication No. WO 2005/121731 A1        
It has however been found that in the case of the sensor equipped wheel support bearing assembly of the construction described above, the strains induced in the outer ring during the passage of the rolling elements are so small that detection with the strain gauge is difficult to achieve. In order to overcome this problem, the use is required of a strain gauge with high sensitivity, resulting in a problem associated with cost increase.
An object of the present invention is to provide a sensor equipped wheel support bearing assembly capable of easily and accurately detecting the load acting on the bearing assembly or the load acting between a vehicle wheel and a road surface.
A sensor equipped wheel support bearing assembly of the present invention is a bearing assembly for rotatably supporting a vehicle wheel relative to an automotive vehicle body, which includes an outer member having an inner periphery formed with a plurality of rolling surfaces defined therein, an inner member having an outer periphery formed with rolling surfaces opposed to the rolling surfaces in the outer member, a plurality of rows of rolling elements interposed between those rolling surfaces, a strain amplifying mechanism for amplifying a strain in a stationary member served by one of the outer and inner members, which strain occurs when the rolling elements pass by, a strain sensor element for detecting the strain amplified by the strain amplifying mechanism, and a calculator for calculating, from an output of the strain sensor element, a load acting on the bearing assembly or a load acting between the vehicle wheel and a road surface.
When a load acts on a wheel support bearing assembly or between a vehicle wheel and a road surface, a strain is induced in the stationary member of the wheel support bearing assembly, but such strain is too low for a strain gauge or the like to detect it directly. However, in the sensor equipped wheel support bearing assembly referred to above, the use is made of the strain amplifying mechanism for amplifying the strain, which is induced when the rolling elements move past one of the outer and inner members serving as the stationary member, and also of the strain sensor element for detecting the strain amplified by such strain amplifying mechanism to thereby increase the sensitivity of detection for the strain. Since as hereinabove described arrangement is made so that the load acting on the wheel support bearing assembly or the load acting between the vehicle wheel and the road surface can be calculated from an output of the strain sensor element by the calculating means, the load acting on the vehicle wheel or the load acting between the vehicle wheel and the road surface can be easily and accurately detected.
In the present invention, the stationary member may be served by the outer member, in which case an outer peripheral surface of the outer member is formed with, at least in an axial range in which the rolling surface of the outer member lies, a thin walled area having a wall thickness smaller than that of a proximity thereof, and the strain amplifying mechanism is provided at the thin walled area. The axial range referred to above, in which the rolling surface lies, is intended to mean a range in which even a portion of the rolling surface is included, and therefore may mean, for example, a range including a portion that is merely radially opposed to an axial end of such rolling surface.
The provision of the thin walled area as referred to above is effective to allow the strain amplifying mechanism to amplify the strain in the outer member which comes to be higher than that in other locations when the rolling elements pass by and, therefore, the detecting sensitivity can be increased correspondingly.
Where the bearing assembly is an angular contact ball bearing, the strain amplifying mechanism is preferably arranged at a location where a line of action of the angular contact ball bearing intersects a radially outward surface of the thin walled area. According to this feature, when the rolling elements move past the thin walled area in the outer member, the strain induced in the thin walled area of the outer member can be effectively amplified by and generated from the strain amplifying mechanism.
The strain amplifying mechanism may include a strain generating member connecting between the thin walled area in the outer member and a portion proximate to the thin walled area, in which case a cutout is provided in a portion of this strain generating member with the strain sensor element provided in the cutout.
In the case of this construction, owing to the cutout, the strain in the outer member can be effectively amplified and transmitted to the location where the strain sensor element is installed and, therefore, the detecting sensitivity can be increased correspondingly.
The thin walled area may include a groove provided in the outer peripheral surface of the outer member so as to extend axially.
The thin walled area may be provided at four locations upwardly, downwardly, leftwards and rightwards of the outer member. If the thin walled area, where the strain amplifying mechanism is provided, is provided at the four locations each arranged upwardly, downwardly, leftwards and rightwards of the outer member, loads acting in various directions can be detected.